Application of Diverse Ground Improvement Techniques for the Stabilization of Reinforced Earth Wall Approach Ramps-Paper

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The paper describes ground improvement for reinforced earth (MSE) approach ramps serving a 635 m elevated structure in Saudi Arabia. The ramps reach heights of 26 m and connect to piled abutments. Site investigations found silty sand and gravel soils with high collapse potential when wetted: 70% of infiltration-test samples showed high potential and 30% moderate potential. Plate-load tests indicated soil stiffness could fall by about 60% after wetting, creating a risk of excessive settlement. A consistent treatment depth of 7 m was therefore adopted beneath the ramp footprint.<br /><br />Treatment was tailored to ramp height and loading. In the highest wall sections (Zones 1 and 4), deep soil mixing (DSM) columns were designed to achieve an average unconfined compressive strength of 1.5 MPa and ground stiffness of at least 200 MPa. The design used 2 m diameter columns on a 2.25 m triangular grid. In lower-wall sections (Zones 2, 3 and 5), the more economical approach combined pre-boring, 900 mm stone columns on a 2.5 m triangular grid, and near-surface densification using Rapid Impact Compaction and High Energy Impact Compaction.<br /><br />Verification results were satisfactory. DSM zone-load tests recorded settlements of 3–5 mm at working load and 5–8 mm at twice working load, below the specified 12.5 mm limit. Compressive-strength testing was also conducted on 360 samples. Post-treatment cone penetration tests in the stone-column zones encountered early refusal within the upper 1–1.5 m, indicating increased ground stiffness.<br /><br />The authors conclude that matching treatment methods to wall height and settlement sensitivity provided robust support near the abutments and cost-effective improvement elsewhere. Most settlement was expected during staged wall construction, with negligible residual settlement after completion.

Keywords

ground improvement

reinforced earth ramps

deep soil mixing

stone columns

collapsible soils

settlement control

Saudi Arabia

MSE walls

piled abutments

rapid impact compaction